fortify: Use __diagnose_as() for better diagnostic coverage

In preparation for using Clang's __pass_object_size, add __diagnose_as()
attributes to mark the functions as being the same as the indicated
builtins. When __daignose_as() is available, Clang will have a more
complete ability to apply its own diagnostic analysis to callers of these
functions, as if they were the builtins themselves. Without __diagnose_as,
Clang's compile time diagnostic messages won't be as precise as they
could be, but at least users of older toolchains will still benefit from
having fortified routines.

Signed-off-by: Kees Cook <[email protected]>
Reviewed-by: Nick Desaulniers <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: kees

include/linux/fortify-string.h

@@ -50,7 +50,8 @@ extern char *__underlying_strncpy(char *p, const char *q, __kernel_size_t size)
 #define __underlying_strncpy	__builtin_strncpy
 #endif
 
-__FORTIFY_INLINE char *strncpy(char * const p, const char *q, __kernel_size_t size)
+__FORTIFY_INLINE __diagnose_as(__builtin_strncpy, 1, 2, 3)
+char *strncpy(char * const p, const char *q, __kernel_size_t size)
 {
 	size_t p_size = __builtin_object_size(p, 1);
 
@@ -61,7 +62,8 @@ __FORTIFY_INLINE char *strncpy(char * const p, const char *q, __kernel_size_t si
 	return __underlying_strncpy(p, q, size);
 }
 
-__FORTIFY_INLINE char *strcat(char * const p, const char *q)
+__FORTIFY_INLINE __diagnose_as(__builtin_strcat, 1, 2)
+char *strcat(char * const p, const char *q)
 {
 	size_t p_size = __builtin_object_size(p, 1);
 
@@ -94,7 +96,8 @@ __FORTIFY_INLINE __kernel_size_t strnlen(const char * const p, __kernel_size_t m
 }
 
 /* defined after fortified strnlen to reuse it. */
-__FORTIFY_INLINE __kernel_size_t strlen(const char * const p)
+__FORTIFY_INLINE __diagnose_as(__builtin_strlen, 1)
+__kernel_size_t strlen(const char * const p)
 {
 	__kernel_size_t ret;
 	size_t p_size = __builtin_object_size(p, 1);
@@ -183,7 +186,8 @@ __FORTIFY_INLINE ssize_t strscpy(char * const p, const char * const q, size_t si
 }
 
 /* defined after fortified strlen and strnlen to reuse them */
-__FORTIFY_INLINE char *strncat(char * const p, const char * const q, __kernel_size_t count)
+__FORTIFY_INLINE __diagnose_as(__builtin_strncat, 1, 2, 3)
+char *strncat(char * const p, const char * const q, __kernel_size_t count)
 {
 	size_t p_len, copy_len;
 	size_t p_size = __builtin_object_size(p, 1);
@@ -365,7 +369,8 @@ __FORTIFY_INLINE void *memscan(void * const p, int c, __kernel_size_t size)
 	return __real_memscan(p, c, size);
 }
 
-__FORTIFY_INLINE int memcmp(const void * const p, const void * const q, __kernel_size_t size)
+__FORTIFY_INLINE __diagnose_as(__builtin_memcmp, 1, 2, 3)
+int memcmp(const void * const p, const void * const q, __kernel_size_t size)
 {
 	size_t p_size = __builtin_object_size(p, 0);
 	size_t q_size = __builtin_object_size(q, 0);
@@ -381,7 +386,8 @@ __FORTIFY_INLINE int memcmp(const void * const p, const void * const q, __kernel
 	return __underlying_memcmp(p, q, size);
 }
 
-__FORTIFY_INLINE void *memchr(const void * const p, int c, __kernel_size_t size)
+__FORTIFY_INLINE __diagnose_as(__builtin_memchr, 1, 2, 3)
+void *memchr(const void * const p, int c, __kernel_size_t size)
 {
 	size_t p_size = __builtin_object_size(p, 0);
 
@@ -417,7 +423,8 @@ __FORTIFY_INLINE void *kmemdup(const void * const p, size_t size, gfp_t gfp)
 }
 
 /* Defined after fortified strlen to reuse it. */
-__FORTIFY_INLINE char *strcpy(char * const p, const char * const q)
+__FORTIFY_INLINE __diagnose_as(__builtin_strcpy, 1, 2)
+char *strcpy(char * const p, const char * const q)
 {
 	size_t p_size = __builtin_object_size(p, 1);
 	size_t q_size = __builtin_object_size(q, 1);